Drok E. High voltage transport of charge carriers in nitride semiconductors heterostructures

The thesis deals with experimental investigation of nitride heterostructures AlGaN/GaN grown on different substrates - sapphire and silicon carbide. The specific features associated with quantum size effects at the interface of semiconductor layers, which are directly formed from the heterostructure, have been studied. Measurements of pulsed current-voltage characteristics in the nanosecond range make it possible to analyze the effect of heating of two-dimensional electron gas. The heating occurs in the case of sufficiently high electric fields. It is shown that additional mechanisms for energy loss carriers appear for so high electric field. An electron drift velocity as high as 1.7 3 1 07 cm/ s was obtained in the fields 160kV/cm. Estimates of thermal budget of the system show that overheating of the electrons exceeds 700 K at highest electric fields achieved in the experiment. The features of kinetic phenomena in heterostructures in the presence of external factors, namely, the electric field and ultraviolet laser radiation were analyzed. The dependence of the electron temperature on the applied voltage was obtained in the range of 4.2K...440K using the method of comparing mobility's. The energy dissipation can be explained by the emission of optical phonons with energy of 90 meV and relaxation time of 25 fs Strong dependence of conductivity on laser irradiation (in UV range) is shown. The dynamics of the conductivity response follows the time evolution of the laser pulse. This fast photoconductivity component shows a considerable enhancement in high electric fields. For the field -15kV/cm, it increases by at least one order of magnitude at temperatures of 4.2 and 300 K. This photoconductivity enhancement is shown to be related to the hot electron effect. The explanation for the observed phenomena was proposed. The mechanism of the photoconductivity enhancement involves nonequilibrium LO phonons generated by hot carriers. Key words: heterostructures AlGaN/GaN, hot electrons, two-dimensional electron gas, electron-phonon interaction.